In B/W i get very nice results with ilford FP4+ 125 exposed at box speed and developed for an extra minute in ID11 1+1 (13 minutes), it gives me superb results and the grain cannot be seen at 12x16 unless you are very close to the paper. If you wanted to go one step further, using it stock virtually eliminates visible grain even at that size. When it comes to colour, i have blown up ektar 100 at that size with no visible grain what so ever and outstanding detail, but detail depends on the quality of your lens as well. I home process my C-41. Portra 160 might be another option but i cannot speak for that one at that size as i have never tried it. I print all of mine optically.
and STAY AWAY from colour plus 200. It is utter crap! no offence, but i got horrible tonal results in nearly every way, unless it was indoors and casual, the moment i took landscapes or high dynamic range scenes in it, i got a very muddy result indeed! I found its latitude terrible if you need that. This was at 8x10, and three different rolls were used, one of which was lab-processed. And a sunset with it looked horrible. I get better results with ultramax 400 but i have never blown it up to 12x16. Ektar if you are going to be shooting landscapes, but it might make skin tones that bit red, in which case, use portra. Have never tried many fuji negative films apart from their consumer ones so cannot speak for those.